Physical activity (PA) is key both to preventing childhood obesity and to reducing an individual's risk for type 2 diabetes (T2D) and certain types of cancer. While conventional PA interventions face problems of sustained motivation and adherence, active video games (AVGs) offer an innovative alternative for PA promotion due to their motivational properties. Although AVGs may allow players to achieve the recommended levels of PA, children's motivation to play AVGs often decreases quickly. To reduce this decline, we introduce an innovative motivating factor: a narrative. A narrative or storyline effectively draws on the human need for narrative closure, i.e., the need to find out how the story will end. A well-constructed narrative has a significant impact on cognition, affect, and health behavior. However, narrative elements are seldom incorporated into AVGs. An AVG with a storyline should encourage children to engage in more PA through increased motivation and extended play. Consequently, AVGs with compelling narratives should increase cognitive and affective AVG evaluation, objectively-measured PA, resulting in better body composition. We plan to explore both the novel addition of compelling narratives to AVGs and the psychological and behavioral consequences on moderate- to-vigorous PA (MVPA). We propose to first identify narrative AVG design strategies to increase PA among ethnically diverse children through 3 Experiments (Expts). Each expt looks at a critical issue regarding the narrative creation. Expt 1 examines which type of plot (continuous/episodic) would result in more MVPA. Expt 2 examines whether ethnically ambiguous characters would result in more MVPA than ethnically specific ones. Expt 3 examines which type of AVG play character (similar/ideal/fantasy) would result in more MVPA among overweight/obese children. We will then use the insight gained from Expts 1-3 to fully develop narratives for 6 AVGs and test their effect in a 3-Group Randomized Control Trial (RCT) among 210 8-12 yo children enrolled in a pediatric obesity intervention over 6 mo; the 3 groups consist of 70 children receiving only the intervention (control group), 70 children who will receive the intervention and also will play the narrative versions of the AVGs by watching corresponding narratives and playing the AVGs, and the last group of 70 will receive the intervention and will play the original versions of the AVGs without narratives. Their body composition, objectively-measured PA, measures of insulin resistance and inflammation derived from fasting glucose and insulin, C-reactive protein (CRP), and fasting lipid profiles as well as cognitive and affective AVG evaluation will be measured. This study is a first step in a series of rigorous systematic inquiries into the behavioral potentials of narratives via AVGs for combating childhood obesity and T2D. Our exploration of narrative's motivating capacities will inspire novel AVG designs and introduce a new dimension of PA facilitation with immersive and inclusive games among diverse children, which may then be translated into school- or family-based health interventions. Such inquiries would help create innovative and effective media products.